neural tube defect. definition failure of closure of the neural tube. can occur at various levels....
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Neural Tube Defect
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Definition
• Failure of closure of the neural tube.
• Can occur at various levels.
• Can have widely varying severity.
• Most severe is anencephaly.
• Least severe is spina bifida occulta.
• Most clincally challenging is lumbo-sacral myelomeningocele.
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Basic Epidemiology
• Varies widely depending on ethnicity and socio-economic status
• ~1% in some places in UK• 1:1000 in US• High in Mexican/Amer-Indian populations.• Virtually all cases are sporadic, isolated
malformations.
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Folate
• Low serum folate correlated with NTDs
• Folate supplementation with 400-800 ug per day reduces incidence by ~75%.
• Clearly, a sub-set of NTDs are not “folate dependent”.
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MHTFR
• 5,10-methylenetetrahydrofolate reductase is in a pathway for recycling folate
• Catalyses a critical step in methionine biosynthesis.
• Several common variants of this enzyme exist.
• Between 5 and 15% of caucasians are homozygous for the variant form.
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• Homozygotes are thought to be at risk for NTD and higher than normal folate supplementation has been recommended.
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Prenatal Detection
• In developed countries, prenatal detection of severe NTD should approach 100%.
• Maternal serum AFP screening is efficient as a screening tool.
• Sonography is efficient at both screening and diagnosis.
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Counseling
• Outcome depends a lot on level.
• Lower lesions may result in relatively mild defecits.
• Another issue is the related hydrocephalus, cerebellar malformation and long-term cognitive dysfunction.
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Downloaded from: StudentConsult (on 15 November 2005 09:42 PM)
© 2005 Elsevier
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Downloaded from: StudentConsult (on 15 November 2005 09:42 PM)
© 2005 Elsevier
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Downloaded from: StudentConsult (on 15 November 2005 09:42 PM)
© 2005 Elsevier
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Summary
• Generally not genetic
• Recurrence risk is elevated over background but still low
• Prenatal detection is excellent but some cases can present a big counseling challenge.